The UCLC is a special purpose amplifier that converts the micro-amp level current output of LI-COR light sensors to an industry standard current-loop level. The UCLC can be configured at the factory or by the end user for any one of three standard LI-COR sensors and any one of two popular current loop levels, through the manipulation of two plug-in jumpers. No soldering or other adjustments are required. The UCLC provides a simple interface between LI-COR sensors and current loop signal processing equipment including data loggers, meters, industrial control equipment, HVAC and green house control systems.
LI-COR sensor Typical full sun response UCLC output (user selectable) LI190 PAR sensor 10µA @ 2000 µE/m2s 1-5 or 4-20mA @ 0.0-12.5µA in LI200 Pyranometer 100µA @ 1000 W/m2 1-5 or 4-20mA @ 0.0-125µA in LI210 Photometer 40µA @ 100 klux (=9290 ftcd.) 1-5 or 4-20mA @ 0.0-50µA in .
Alternate settings are available on special order. The calibration tag provided by LI-COR with each sensor in conjunction with the UCLC gain setting can be used to compute the light level incident on the sensor with a high degree of accuracy.
On
the UCLC shown in the photo, the input cable from the sensor will
enter through the gland nut to the left, and the output cable to the
equipment will exit through the gland nut on the right. The UCLC
is also available with a BNC connector on the input. The
calibration label on the outside of the enclousure is marked with the
applicable gain setting. Wiring instructions and calibration notes
are included with each UCLC.
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In order to convert the UCLC's loop current into your sensor's units of light, you will have to program your equipment to multiply LI-COR sensor's calibration constant (printed on the calibration tag that accompanies each individual LI-COR sensor), times the net loop current, divided by the UCLC's gain in milliamps per microamp.
Net loop current is the second term on the right, equal to the total loop current minus the offset current. The UCLC has an offset current of either 1mA or 4mA depending on the jumper setting. Refer to the chart below to find the current loop gain corresponding to the jumper position you have selected for your UCLC. Refer the the calibration tag on your LI-COR sensor for the conversion factor for your particular sensor.
Table of Current loop gain for various jumper settings and for LI-COR sensor types.
JP1 | 1-5 ma 4-20 ma }JP2 position LI-190 | 0.320 ma/µA 1.280 ma/µA \ LI-200 | 0.032 ma/µA 0.128 ma/µA }UCLC gain LI-210 | 0.080 ma/µA 0.320 ma/µA /
The LI-COR sensor connects to the input, either to the BNC connector (SA series) or to the two screw-down terminals (SZ series). If the internal terminals are used, the coaxial cable from the sensor passes through a gland nut. The output of the UTA connects to your equipment via a three-wire cable, with +V (5 to 25 volts DC), signal, and common. The three conductors attach to the color-coded terminals inside the UTA enclosure and the cable passes through a gland nut. In electrically noisy environments, it may be desireable to use shielded cable. The enclosure has mounting holes outside the gasket for securing the enclosure to a backplane if desired.
Example 1: Suppose you will be using your UCLC in conjunction with a Quantum PAR sensor (LI-190), and that its individual calibration tag that states a conversion factor of 187.5µE/m2s per µA. You use a the 4 to 20 mA loop. The proper gain setting for your UCLC is 1.28 mA/µA (1st row , 2nd column in above table). The conversion is: light level in µE/m2s = [(net loop current) / 1.28]* 187.5 = (net loop current)*(146.48 µE/m2s per mA) . If the total current level happens to be 10.0 ma, the net loop current is 6 ma, so the light level is 878.88 µE/m2s.
Example 2: Suppose you will be using your UCLC in conjunction with a Pyranometer sensor (LI-200), and that its individual calibration tag that states a conversion factor of 9.8W/m2 per µA.. You choose a 1 to 5 mA current loop. The proper gain setting for your UCLC is 0.032 mA/µA (2nd row, 1st column in above table). The conversion is: light level in W/m2= [(net loop current)/0.032] * 9.8 = (net loop current)*(306.25 W/m2 per mA ) . If the total current happens to be 5 ma, the net loop current is 4 ma, so the light level is 1225W/m2.
Example 3: Suppose you will be using your UCLC in conjunction with a Photometer sensor (LI-210), and its individual calibration tag that gives a conversion factor of 2.42 klux/µA. You use a 4 to 20 mA current loop. The proper gain setting for your UCLC is 0.32 mA/µA (3rd row, 2nd column in above table). The formula is: light level in klux = [(net loop current)]/0.32]*4.82 = (net loop current)*(7.56klux per mA). If the total current happens to be 17 ma, then the net loop current is 13 ma, so the light level is 98.28 klux. Note: 1 footcandle = 10.76 lux.
It is also possible to calibrate UCLCs to match an individual LICOR sensors. For example, you might want the output of the LI200/UCLC matched pair to be exactly 20 ma when the input is 1280 watts per meter squared. If the sensor and amplifier are matched in this way, then the individual calibration does not have to be entered in software. Please consult the the instructions that come with the UTA amplifier or request special factory calibration.
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>![Light = [UCLC_cal] * [(total_mA) - (offset_mA)] / [UCLC_gain]](images/uclc/uclc_eqn.gif){kind=small}